300 i6 idle adjusting
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300 i6 idle adjusting
I have an '85 f250 with a 300 straight six in it, all engine parts are stock except for an aftermarket air cleaner. The truck is great and runs perfect... once it is warm. Even in this warm weather I have to press the gas pedal in to set the choke, last summer I didn't. I would like to set the cold idle a bit higher as it is only around 750-800 currently and it just doesn't seem high enough to warm it up I believe that this should fix my final issue with it but I am open to any other idea that someone with higher knowledge than I have which is just about anyone as I am not a trained mechanic. Thanks for any help or advice you may be able to offer.
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Joined: Jan 2001
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From: Virginia
I can't explain why you didn't have to set the choke before, but setting the choke by pressing the pedal at least once is standard procedure. The choke mechanism usually does not have enough power to overcome the throttle spring pressure and let the fast idle cam slide without pushing in on the throttle to relieve the pressure. It's especially hard for it to go up by itself over the steps in the cam.
Some carbs will not let you adjust the fast idle easily, some do. Look around and underneath the round black piece on the carb. There could be a adjusting screw under there that hits the cam. The cam will look like a flat plate with steps on it. Tweak this screw and it will adjust the fast idle without affecting the normal idle after it's warmed up.
Some carbs will not let you adjust the fast idle easily, some do. Look around and underneath the round black piece on the carb. There could be a adjusting screw under there that hits the cam. The cam will look like a flat plate with steps on it. Tweak this screw and it will adjust the fast idle without affecting the normal idle after it's warmed up.
Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
I am going from memory, so I hope I remember right...
Remove the air cleaner so you can see more clearly. From the driver's side fender, look at the carburetor. On the right side [toward back of truck] near where the throttle cable attaches, there will be two screws [one on top of the other]. The one which lines up with the stepped cam [as mentioned by Franklin2] controls the speed of the fast idle. Turning the screw clockwise will increase the speed.
Use carburetor cleaner and make certain none of the pivot points and linkage are binding.
While the air filter is off, use this opportunity to take a 1/2" wrench and check the two bolts which hold the carburetor down. They tend to vibrate loose and will cause a lean running condition. Do not overtighten!
Look at all vacuum hoses and vacuum ports as they tend to crack or fall off.
Welcome to the forum!
Remove the air cleaner so you can see more clearly. From the driver's side fender, look at the carburetor. On the right side [toward back of truck] near where the throttle cable attaches, there will be two screws [one on top of the other]. The one which lines up with the stepped cam [as mentioned by Franklin2] controls the speed of the fast idle. Turning the screw clockwise will increase the speed.
Use carburetor cleaner and make certain none of the pivot points and linkage are binding.
While the air filter is off, use this opportunity to take a 1/2" wrench and check the two bolts which hold the carburetor down. They tend to vibrate loose and will cause a lean running condition. Do not overtighten!
Look at all vacuum hoses and vacuum ports as they tend to crack or fall off.
Welcome to the forum!
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